Embed Perl in other C program is not difficult, but mod_perl is much more than just Perl inside apache. mod_perl works directly with Apache, and you can handle and control a lot of behaviors of Apache from Perl.

But I don't want to discourage you. Soo, first perlembed in your App. Than you need to redirect the output of Perl to the socket of the client, without forget the reverse of that, the input (STDIN). Well, I think that you have done something like that for CGI.

After do the IO work, you need to overwrite exit() and die(), since you can't let the Perl script to close or dump your server. And the work goes. Soo, you will need to like to hack the Perl internals.

Also you can do a lot of this changes with pure Perl, since the language let you change the Perl interpreter behavior. Soo, here are some modules that can help you to do the pure Perl changes:

Also you can talk with the mod_perl folks. They can help you, or give you some light.

Good luck! ;-P